A gas turbine engine compressor is effective for providing compressed or pressurized airflow to a combustor wherein it is mixed with fuel for undergoing combustion for powering the engine. The compressed airflow is discharged from the compressor at a relatively high velocity and, therefore, a diffuser is typically utilized for decreasing the velocity of the compressed airflow while increasing the static pressure thereof, which is known as pressure recovery, for obtaining more efficient operation of the combustor and engine. A conventional diffuser has an inlet and an outlet defined between diverging walls with an effective area ratio of the outlet area over the inlet area for obtaining diffusion. The diffuser also includes a length from the inlet to the outlet and the inlet has a specific height.
The amount of divergence of the diffuser walls is relatively small with a relatively small corresponding area ratio to ensure that diffusion occurs without undesirable flow separation from the walls which results in conventionally known stall which adversely affects performance of the diffuser. The conventionally known Stanford criteria are used for optimizing the area ratio for particular diffusers as a function of the length to height ratio. For a given length to height ratio, a maximum area ratio is required for preventing flow separation in the diffuser and maintaining an acceptable flow separation, or stall margin.
In order to reduce the length of the diffuser, it is conventionally known in the literature to provide a diffuser having multiple diffusing channels, for example two diffuser channels separated by a circumferentially extending splitter. In a multi-channel diffuser, the compressed airflow from the compressor is divided by the splitter and portions thereof are channeled in parallel through the several channels for separately diffusing the airflow portions. Although each channel is smaller than the original single channel which would otherwise be required, each channel can still have the same length to height ratios and equal area ratios for maximizing pressure recovery with acceptable flow separation margin. The several multi-channels, which are relatively shorter than a corresponding single channel diffuser, can thus collectively provide the same amount of total pressure recovery from the airflow.
However, a multi-channel diffuser is inherently more complex than a single channel diffuser and is similarly subject to pressure losses during operation which decrease efficiency of the diffuser and decrease pressure recovery, and is also subject to flow separation at the four walls defining the two channels.
Furthermore, a diffuser is typically designed for operation of the compressor at a particular design point, or velocity condition of the discharged compressor airflow. During the life of the gas turbine engine and compressor, normal wear of the engine results in changes to the designed-for velocity condition of the discharged compressor airflow, which in turn affects performance of the diffuser including pressure recovery and stall margin.